Conventional Ziegler-Natta Catalysts based on Magnesium halide and titanium halide compounds have advantages of easy control of the morphology of polyolefin, however, when they are employed in the process of copolymerization, they tend to produce copolymers having broad compositional distribution, resulting in inadequate physical properties in impact strength, transparency, antiblocking, and in heat-sealing temperature. Metallocene catalysts have been developed which show excellent copolymerization properties such as impact strength, transparency, anti-blocking, and heat-sealing temperature. Recently, metallocene compounds with special substituents, which can control the electronic or steric environment of olefin polymerization, and the stereoregularity and molecular weight of polymer, have also been developed. But still they have several such disadvantages, when applied in a commercial plant, such as complicated synthetic steps, additional capital investments, the need to modify existing processes and poor processibility due to this narrow molecular weight distribution.
Meanwhile, several inventions have been made employing oxygen or heteroatom-bound chelated transition metal compounds, and they have attracted keen attention, because these compounds are easier to synthesize than metallocene compounds, and may be used as an alternative to metallocene compounds.
Japanese Laid-Open Patent Sho 63-191811 disclosed the chelated catalysts for ethylene and propylene polymerization, in which chlorides of titanium chloride compound are replaced by TBP ligand (6-tert butyl-4-methylphenoxy). With a methylaluminoxane (MAO) cocatalyst, it was reported, polymerization of ethylene and propylene with excellent activity and a high molecular weight (Mw=3,600,000) was possible. U.S. Pat. No. 5,134,104 to Sasati, et. al. reported chelate catalysts employing an amine substituted titanium halide compound, {(C.sub.8 C.sub.17).sub.2 NTiCl.sub.3 } and the results of olefin polymerization with these catalysts, while in J. Am. Chem. Soc., 117, 3008, catalysts using oxygen-bound chelated transition metal compounds which localize the coordination sphere of transition metal compounds were introduced. Also transition metal compounds chelated with phenoxy derivative ligands were reported in Japanese Laid-Open Patent Hei 6-340711 and EP 0606125A2, which, with MAO as cocatalyst, produced a high molecular weight polymer which has a narrow molecular weight distribution.
Recently, several transition metal compounds chelated with carbodiimide ligands have been publicized. Synthesis and characterization of titanium compounds containing carbodiimide ligands were reported in Organometallics 1996, 15,2627 and Chem. Commun. 1996, 2623, and chemistry of carbodiimide compounds was introduced in Coord. Chem. Rev. 1994, 137,403, Inorg. Chem. 1997, 36,501, and Inorg. Chem. 1996, 35,1423. Also, U.S. Pat. No. 5,502,128 to Flores, et. al. disclosed a homogeneous catalyst system employing transition metal compounds, carbodiimide ligand with MAO as cocatalyst.
However, the synthetic methods reported so far require additional separation procedures for lithium chloride or complicated synthetic routes to prepare pure carbodiimide compounds, and these catalyst systems, being homogeneous catalyst systems, still require the expensive MAO as a cocatalyst to polymerize olefin, and the copolymerization properties of these compounds have never been reported. Nor has there been reported an example of heterogeneous catalyst systems employing transition metal compounds chelated with carbodiimide ligands, which can control the morphology of polymer.